Dynamic Thread Sharing in Branch Prediction Structures

1. A computer implemented method for dynamically evaluating how to share, among threads that are being tracked in a processor circuit, entries of a multithreaded branch prediction structure, the method comprising: receiving a search request to locate branch prediction information associated with said search request; searching, by said processor circuit, in a first-level branch prediction structure for conditionally matching first-level entries corresponding to the search request; said first-level entries each including a thread state; wherein the thread state comprises a first thread state portion having at least one data field that identifies either a share-state or a no-share state of threads that are being tracked in the processor circuit; wherein the thread state further comprises a second thread state portion having at least one data field that identifies context thread information of threads that are being tracked in the processor circuit; wherein conditionally matching first-level entries corresponding to the search request comprises satisfying either of a first condition or a second condition; wherein satisfying said first condition comprises determining that said at least one data field of said first thread state portion identifies said share-state; wherein satisfying said second condition comprises determining that said second thread state portion matches a portion of the search request; initially allowing, by said processor circuit, said conditionally matching first-level entries; and not allowing, by said processor circuit, specific ones of said conditionally matching first-level entries based on determining that said specific ones of said conditionally matching first-level entries previously caused a problem on at least one of threads corresponding to said thread states of said specific ones of said conditionally matching first-level entries.

2. The computer implemented method of claim 1 further comprising, in response to said problem, updating said first thread state portion of said each first-level entries.

3. The computer implemented method of claim 1 wherein said problem comprises a bad branch presence prediction associated with said at least one of the threads.

4. The computer implemented method of claim 1 wherein said first portion of said thread state comprises setting a thread sharing data field.

5. The computer implemented method of claim 1 wherein said at least one data field that identifies context thread information comprises a thread context tag.

6. The computer implemented method of claim 5 wherein: said determining comprises identifying a conflict mode; and said conflict mode comprises a mismatch between said thread context tag and said context state information.

7. The computer implemented method of claim 1 wherein: said branch prediction structure is hierarchical and includes: a second-level branch prediction structure; and the processor circuit communicatively coupled to the second-level branch prediction structure, wherein the method of claim 1 further comprises: based on failing to locate a matching first-level entry in the first-level branch prediction structure corresponding to the search request, initiating, by the processor circuit, a secondary search to locate matching second-level entries in the second-level branch prediction structure; said second level entries each including a second-level thread state; initially allowing, by said processor circuit, said conditionally matching second-level entries; and not allowing, by said processor circuit, specific ones of said conditionally matching second-level entries based on second-level threads state of said second-level specific ones indicating that said second-level specific ones of said conditionally matching second-level entries previously caused a problem on at least one of the threads corresponding to said second-level thread states.